The present invention relates to protective and decorative moldings made of plastic resin or rubber. More specifically, the invention relates to a hollow molding with adhesive layer on the rear surface to utilize adhesive force of the layer and prevent failure of adhesion.
So-called hollow molding, i.e. molding having hollow portion inside the molding body has been used in automobiles or the like for the purpose of weight reduction, absorption of shock force or saving of raw material.
Particularly in moldings for automobiles, use of larger size is seen in recent years. Molding of larger size even in hollow type inevitably increases in weight. Since necessary rigidity and strength limit material and size, increase of weight results in decrease of adhesive force in the adhesive layer. In addition, the adhesive layer usually comprises double-coated adhesive tape.
The decrease of adhesive force in large-size hollow molding is significantly seen in automobiles. Automobiles are subjected to thermal variation in higher or lower temperatures and influence of vibration from the use condition and environment, and as the size of molding increases the variation in expansion and depression and the vibration significantly influences the adhesive force.
It is found that the decrease of adhesive force occurs from another reason hereinafter described. Referring to FIG. 12, conventional hollow molding 11 comprises a molding body 12, a hollow portion 13 constituted within the body 12, and an adhesive layer 14 on the rear surface. The molding body 12 comprises a front surface 15, a side portion 16, and a bottom 17. When the hollow molding 11 is pushed against a substance A for adhesion using a jig B such as a roll, both side ends are apt to be moved upwards as shown in FIG. 13. Therefore the pushing force for adhesion is not applied sufficiently to both side ends. The reason therefore is described as follows.
Referring to FIG. 14, when the molding is pushed by the roll, the contact pressure F in the vertical direction and the bending moment MF act between the front surface 15 and the side portion 16. Against the contact pressure F and the bending moment MF, reaction W towards the front surface and reactive moment MW act on the adhesive layer 14 of the bottom 17. If the contact pressure F and the reaction W act in a line, of if the reaction W is to the side of the bending moment MF, the bending moment MF and the reactive moment MW are suppressed and decreased, thereby the pushing force applied to the molding front surface 15 is transmitted properly to the adhesive layer 14 and sufficient adhesive force is obtained. In the opposite conditions to the above described, however, the bending moment increases and most of the pushing force applied to the molding acts as the bending moment and the reactive moment, thereby the molding body is moved upwards at both side ends as shown in FIG. 13 and sufficient contact pressure is not transmitted to the adhesive layer, resulting in failure of adhesion.
Referring to FIGS. 15 and 16, relation of the contact pressure and the bending moment will be described in detail. The pushing force applied by a roll or the like acts as the contact pressure F at the point of action of force P and the bending moment MF at the fulcrum Q. The contact pressure F is distributed in plane pressure distribution (arrow designation) as shown in FIG. 15. The plane pressure W attenuates from the point of action of force towards both side ends. The plane pressure at the hollow portion is negligible. Relation between the contact pressure F and the plane pressure W is represented by following equation. EQU .intg.wdx+F=0
That is, addition of integration of the plane pressure W and the contact pressure F becomes 0. Relation between the bending moment MF and the plane pressure balanced to this is represented by following equation. EQU .intg.w.multidot.xdx+MF=0
That is, addition of the bending moment and the plane pressure balanced to this becomes 0.
The plane pressure in summation of components of FIG. 15 and FIG. 16 contributes to adhesion in the adhesive layer. If the pressure acting towards the rear surface of molding is positive, it directly contributes to the adhesive force; if negative, it acts to peel the molding from adhesive state. Now, state of various portions in conventional hollow molding will be studied by summing the plane pressure distribution corresponding to the contact pressure and the plane pressure balanced to the bending moment. At the point of action of force P, since the fulcrum Q of the bending moment is disposed to the bottom, the plane pressure balanced to the bending moment becomes 0 thereby the plane pressure (positive) corresponding to the contact pressure contributes to the adhesive force completely. Going from the point P towards the end of the molding side portion, since the plane pressure (positive) corresponding to the contact pressure decreases and the plane pressure (negative) balanced to the bending moment increases, pressures contributing to the adhesive force significantly decreases. At the end, the plane pressure distribution (positive pressure) corresponding to the contact pressure becomes approximately zero and only the plane pressure (negative pressure) balanced to the bending moment acts, thereby pressure contributing to the adhesive force becomes negative and acts to peel the molding, resulting in upward movement of both ends of the molding side portion as above described.